The date that the castle was built is unclear.[1] Between 1154 and 1175 it was in possession of the Earl of Cornwall and it had become a royal possession by 1185. Both Henry III and John spent money on the castle.[2] It appears to have been disused from about 1290 and there are references to its stonework being reused by the Chidlock family to build Dorchester Greyfriars in 1309.[2][3][4][5] Certainly it was abandoned by 1422.[6]
Dorchester Prison occupies its site – originally to the north of the town, with a Franciscan Priory further east, but nothing of the castle or the priory remain.[7] However, in 1720, two underground passages were discovered while building a chapel: these once connected the castle to the town proper.[8] In the 1800s, a bastion-like rampart still existed, and a small rampart and ditch were visible on the north and east sides.[8] The gatehouse was built in 1790 and has been designated as a Grade II listed building.[9]
